Color tube degausser



Oct. 25, 1966 s. KAPLAN ET AL COLOR TUBE DEGAUSSER Filed Aug. 5, 1964 FIG.2

able hand-actuated device of United States Patent 3,281,742 COLOR TUBE DEGAUSSER Samuel Kaplan, Oak Park, and John L. Rennick, Elmwood Park, Ill., assignors to Zenith Radio Corporation, Chicago, III., a corporation of Delaware Filed Aug. 3, 1964, Ser. No. 387,109 2 Claims. (Cl. 335-284) This invention relates in general to demagnetizing apparatus and in particular to a portable device for degaussing the shadow-mask of a cathode-ray tube.

The electron beam of a cathode-ray tube, especially a tube employing a significant mass of magnetizable material in close proximity to the beam path, is particularly susceptible to the influences of a magnetic field. When subjected to the earths magnetic field or any other magnetic field, the random orientation of the atomic structure of the magnetizable material within the tube can become polarized in such a fashion that the material assumes the properties of a permanent magnet which necessarily influences the beam travel.

This effect may be experienced particularly in the shadow-mask type of color reproducing cathode-ray tube which employs a color-selection barrier or shadow-mask of magnetizable material having the same overall dimensions as the tube screen. This mask i mounted immediately behind and adjacent the screen of the tube and if it becomes magnetized, the electron beams are deflected from their intended trajectories and impinge improperly on the color-dot clusters. This misregistration of the beams relative to the dot cluster manifests itself as color impurity.

Ordinarily, the influence of the earths magnetic field upon a color tube is neutralized when the receiver is initially installed by demagnetizing or degaussing the tube at that time. The degaussing apparatus usually employed comprises a coil which is energized from a 110 volt AC. outlet to develop a fluctuating magnetic field. The coil is swept back and forth across the face of the cathode-ray tube so that the fluctuating field may penetrate the shadow-mask and return its atomic structure to a random state. However, if the television receiver is subsequently moved so that the electron beams of the tube assume a different orientation with respect to the earths magnetic field, the tube may require further degaussing in order to preclude color impurity. Degaussing in this manner, however, entails a service call.

It has been suggested that a degaussing coil and energizing circuit be installed as a component of the color receiver with a switch that may be actuated to degauss the tube. While this is a satisfactory solution to the problem, it entails an expense that may oftentimes be unjustified.

It is, therefore, an object of the invention to provide a portable device for degaussing 1a cathode-ray tube.

It is a more specific object of the invention to provide a portable self-contained device for degaussing the shadow-mask of a color reproducing cathode-ray tube.

It is also an object of the invention to provide a porteconomical construction for degaussing a cathode-ray tube.

In accordance with the invention, a portable handactuated device for degaussing a cathode-ray tube comprises a disc of magnetic material having a central aperture and magnetized to exhibit a magnetic north pole and a magnetic south pole. These magnetic poles are located at diametrically opposed positions on the periphery of the disc. The device also includes a mounting bracket and a shaft which is secured to the bracket and extends into the disc aperture to support the disc for free rotation relative to the shaft. Finally, a handle is provided which extends from the bracket.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a plan view of a degaussing device embodying the invention;

FIGURE 2 is a plan view of a magnetic disc employed in the device of FIGURE 1; and

FIGURE 3 is a side view, partly in section, taken along lines 33 of FIGURE 1.

The degaussing device 10 shown in FIGURE 1 comprises a disc 11 of magnetic material, preferably a homogeneous mass of ferrous material having a central aperture 12 extending there-through. As schematically depicted in FIGURE 2, disc 11 is magnetized in such a fashion as to exhibit a magnetic north pole N and a magnetic south pole S, which poles are effectively located at diametrically opposed positions on the periphery of disc 11. While disc 11 may be magnetized to provide additional pairs of poles, it has been found that a magnetic disc having a single pair of poles performs entirely satisfactorily for degaussing the shadow-mask of a color tube.

Disposed about the periphery of disc 11 is a ring-like pad 13 of vinyl or other suitable plastic which serves to not only protect the peripheral surface of magnetic disc 11 but also to prevent the disc from marring a surface in which it is intended to come in contact.

The degaussing device includes a U-shaped mounting bracket 14 which captivates a shaft or axle 15 that spans the bight portion of the bracket. As best shown in FIG- URE 3, shaft 15 extends through aperture 12 of disc 11 and serves as a mount for rotatably supporting the disc. A handle 16 is secured to the bight portion of bracket 14 by a suitable fastener.

To degauss or demagnetize a shadow-mask type of a color reproducing cathode-ray tube with device 10, the operating merely grasps handle 16, firmly presses the periphery of disc 11 against a solid surface and draws the disc across that surface with suificient force to spin the disc. Since the disc is mounted to be freely rotatable, it will rotate for a considerable period of time and its rotation effectively generates an alternating magnetic field. While the disc is still spinning, it is swept back and forth and up and down across the face of the cathode-ray tube and as close to the faceplate as practicable. If the component parts of the degausser are covered with a soft material or are constructed from a soft material that will not scratch the glass screen surface of the receiver, the degausser may be passed over the screen surface. In any event the alternating field penetrates to the mask as required to accomplish degaussing. While the disc is still spinning, it is gradually withdrawn away from the face of the tube. In some instances it may be necessary to repeat this procedure several times to achieve sufiicient degaussing to restore color purity.

While the demagnetizing device has been shown as a simple hand-actuated device, it is appreciated that a more sophisticated structure can be resorted to in which the magnetic disc 11 is driven by a small D.C. powered motor. Disc 11 is of such a small size, about 1%, that the entire structure can he fitted inside the casing of a conventional two-cell flashlight, thus retaining the hand-actuated and portability features. In either case, degaussing of a cathode-ray tube is achieved by sweeping a spinning bipolar disc of magnetic material in proximity to the magnetizable structure of the tube.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

We claim:

1. A portable hand-actuated device for degaussing a cathode-ray tube comprising:

a disc of magnetic material having a central aperture and magnetized to exhibit a magnetic north pole and a magnetic south pole located at diametrically opposed positions on the periphery of said disc;

a mounting bracket;

a shaft secured to said bracket and extending into said aperture and supporting said disc for free rotation relative to said shaft;

and a handle extending from said bracket.

2. A portable hand-actuated device for degaussing the shadow-mask of a color reproducing cathode-ray tube comprising:

References Cited by the Examiner UNITED STATES PATENTS 2,903,689 9/1959 Scanlon 3l7200 X BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, JR., Assistant Examiner. 

1. A PORTABLE HAND-ACTUATED DEVICE FOR DEGAUSSING CATHODE-RAY TUBE COMPRISING: A DISC OF MAGNETIC MATERIAL HAVING A CENTRAL APERTURE AND MAGNETIZED TO EXHIBIT A MAGNETIC NOTH POLE AND A MAGNETIC SOUTH POLE LOCATED AT DIAMETRICALLY OPPOSED POSITIONS ON THE PERIPHERY OF SAID DISC; A MOUNTING BRACKET; A SHAFT SECURED TO SAID BRACKET AND EXTENDING INTO SAID APERTURE AND SUPPORTING SAID DISC FOR FREE ROTATION RELATIVE TO SAID SHAFT; AND A HANDLE EXTENDING FROM SAID BRACKET. 